High volume automated manufacturing systems are very good at producing large numbers of identical interchangeable parts. However, unless there is adequate inspection of the output of these systems, if they drift out of compliance and start producing parts that are out of tolerance or start producing defective components due to chipped tools or other causes, they can produce very large quantities of identical defective parts before the problem is detected. The material from which a part is produced can also contain defects, such as pores or scratches that would cause a finished part to be rejected as defective.
If defective components enter the assembly stream for a manufactured product, such as a vehicle or appliance, the cost of detecting and correcting a defect can increase exponentially. This cost includes the cost of detecting the problem, disassembling the product to identify the component causing the problem, and identifying and correcting the source of the component defect. It may involve shutting down a production line until the source of the problem is identified and corrected. If finished products are shipped with defective components, the cost of fixing the problem could also involve product returns and warranty repairs.
There is, therefore, a high priority placed on identifying defective components at the earliest possible stage of production to minimize scrap and prevent defective components from entering the assembly stream. In a high volume automated production system inspection of parts by human inspectors is subjective and inadequate. It is preferable to have inspection techniques that can be automated to detect defects at the rate of production according to objective criteria. Non-contact inspection methods are preferred because they do not involve the use of mechanical gauges that can wear and need to be periodically replaced. Optical inspection of components is one of these non-contact inspection techniques. It is often preferred for detecting surface defects in manufactured components because it can rapidly collect and analyze high resolution data.
A number of non-contact optical devices have been developed over the past several years for the inspection of manufactured surfaces in a production environment. These can be divided into two broad categories according to the light source that is used—laser scanning devices and machine vision systems employing broadband unpolarized or white light sources. Each of these two approaches to optical inspection can be divided into two main classes of devices—those that inspect the exterior surfaces of components and those that inspect the interior surfaces. Devices that inspect exterior surfaces that are flat or have a curved profile may not be capable of inspecting the interior surfaces of cylindrical objects. Some vision systems developed for external inspection can see inside containers, but their inspection capabilities are limited, especially if a container is long and narrow, such as the case of some cylinders. However, inspection systems that can inspect the inside of cylinders may be adapted to measure the outside of cylindrical or cylindrically symmetric objects, disks or spheres.
Accordingly, there is a need in the art for an improved non-contact laser inspection system capable of rapidly detecting surface defects and surface profile variations using laser light to inspect cylinder bores.